Plate-making master and method for producing a printing plate which does not require dampening water

ABSTRACT

A planographic printing plate that does not require dampening water during printing is prepared by electrophotographically forming an ink-receptive portion and an ink-repelling portion on a plate-making master comprising a support, a photoconductive substance and a silicone rubber thereon, either as two separate layers or as a mixed layer.

United States Patent Kondo et al.

PLATE-MAKING MASTER AND METHOD FOR PRODUCING A PRINTING PLATE WHICH DOES NOT REQUIRE DAMPENING WATER Inventors: Asaji Kondo; Shinzo Kishimoto;

Kenichiro Yazawa; Shizuo Miyano; Satoru I-Ionjo, all of Saitama, Japan Assignee: Fuji Photo Film Co., Ltd.,

Ashigara-shi, Kanagawa, Japan Filed: May 15, 1973 Appl. No.: 360,511

Foreign Application Priority Data May 15, 1972 Japan .7 47-47977 US. Cl. 96/] R, 96/33 Int. Cl. G03g G03f 7/02 Field of Search 96/33, 1 R

OTHER PUBLICATIONS G.E. Silicones, Pubn. CDS-129G. Revised-11/67, G. E. Silicon Products Dept, Waterford, N.Y. p. 5.

Primary E.\'aminerDavid Klein Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT A planographic printing plate that does not require dampening water during printing is prepared by electrophotographically forming an ink-receptive portion and an ink-repelling portion on a plate-making master comprising a support, a photoconductive substance and a silicone rubber thereon, either as two separate layers or as a mixed layer.

14 Claims, 6 Drawing Figures PATENTEUHAR 4151i FIGS m w m PLATE-MAKING MASTER AND METHOD FOR PRODUCING A PRINTING PLATE WHICH DOES NOT REQUIRE DAMPENING WATER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for producing a printing plate that can be prepared electrophotographically and does not require dampening water during printing, and to a master plate for this plate making. More specifically, it relates to a method for producing a printing plate that doesnot require dampening water, which comprises electrophotographically forming an ink-receptive portion and an ink-repelling portion on the surface of a master plate comprising a support, a layer of a photoconductive substance and a layer of a silicone rubber, both formed on said support.

2. Description of the Prior Art Planographic printing is a macroscopic classification made in comparison with relief printing and intaglio printing, but microscopically, it does not employ a completely plane plate. A typical example is offset printing.

The master plate from which a printing plate can be prepared electrophotographically does not have photosensitivity by itself, but can be rendered photosensitive by electrostatically charging it in a dark place. Examples of such master plate are Elefax master plate (a master plate for electronic plate maker, lwasaki Tsushinki Kabushiki Kaisha), Electronic Ricopy Master (Ricoh Kabushiki Kaisha), Electrostatic Image Master (AM Company, U.S.A.), and other commercially available master plates manufactured by Xerox Company, Tokyo Koku Keiki Kabushiki Kaisha,-Canon Kabushiki Kaisha and Konishiroku Shashin Kogyo Kabushiki Kaisha.

These masters comprise a support and a layer of a photoconductive polymer or a layer of a kneaded mixture of a photoconductive substance and an insulating binder formed on the support. The master is charged in a dark place by corona discharge, and exposed imagewise through an original by the reflex or transmission method. The charge decays rapidly at the exposed portions, but remains at the unexposed portions to form an imagewise charge pattern. When the charge pattern is developed and fixed by a toner, the pattern of the original is reproduced. The ink-affinitive toner adheres to the portion corresponding to the image area of the original, and the portion corresponding to the non-image area becomes hydrophilic. The printing plate thus formed electrophotographically is placed on an offset printing press, and printing is carried out while feeding dampening water.

These planographic master plates that can be electrophotographically formed into printing plates have a number of advantages such as high sensitivity, no need for an intermediate negative, easy and short plate making procedure, availability both in negative and positive working, absence of photosensitivity unless charged in a dark place and long shelf life. However, since the difference between the hydrophobicity of the image area and the hydrophilicity of the non-image area is not so great, it is essential to impart dampening water to the non-image area during printing so as to prevent the adhesion of oily ink thereto.

It is well known that the procedure of applying dampening water has great importance in planographic printing now in use, represented by offset printing. Specifically, expert skill and control are required to balance the supply of dampening water and oily ink. There is also a restriction on the manufacture of the printing ink so as to prevent the mixing of the dampening water with the oily ink toform an emulsion. The elongation or shrinkage of printing paper due to the dampening water also poses a problem. These problems accompanying the use of dampening water are also significant with presensitized planographic printing plates in general, that is, printing plates including a photochemically sensitive substance which undergoes a reaction such as a decomposition, polymerization or cross-linking reaction by the action of heat, such as a diazonium compound, quinonediazide compound or photopolymer as the photosensitive substance.

Techniques have been developed for. omitting the use of dampening water in offset printing by using presensitized plates on'the surface of which a layer of a pure silicone rubber is formed (for example, Japanese Pat. Publications Nos. 23042/69 and 16044/71, and US. Pat. Nos. 3,511,178 and 3,606,922). Such printing plates are described in the Japanese language publication Printing Journal, Vol. 53, October 1970, page 48 and November 1970, page 51,. and are sold under the tradename DRYPLATE. The principle of these techniques lies in the fact that only the non-image area of the surface of the printing plate is covered by silicone rubber which has a high rep ellancy for oily ink, whereupon the image area receives ink but the nonimage area repels it, and the supply of dampening water is not required.

These dry plates were very significant in that they solved the problem of dampening water supply. However, since they are based on conventional presensitized plates including photochemically sensitive substances, they cannot be free from the defects of the conventional presensitized plates such as low sensitivity, the necessity of an intermediate positive or negative, the necessity of storage in a light-shielded place, a complex processing procedure and a short shelf life.

SUMMARY OF THE INVENTION Another object of this invention is to provide a method for producing a printing plate that does not require dampening water during printing, which comprises electrophotographically treating this master plate.

The inventors of the present invention performed various experiments with a view to producing plano graphic printing plates which possess the merits of an electrographically formed master plate and a dry plate produced by coating a silicone rubber layer on a presensitized plate, and obtained the following results, from which the present invention was arrived at.

1. When a conventional master plate for electrophotographic plate-making comprising a support and a photoconductive layer formed thereon (the thickness of this layer is preferably 0.5 ,u, most preferably 1 2 ;1.; commercial master plates are available which comprise a pigment/resin dispersion type photoconductive layer, in which the ratio of zinc oxide insulating binder is about 8/1) is coated with a layer of silicone rubber in a thickness of not more than microns, preferably about 2 to 5 microns, there can be produced a printing plate having sufficient electrophotographic plate-making properties, and having a superior ability of repelling ink without the supply of dampening water.

2. When a photosensitive layer (electrophotographically rendered photosensitive, i.e., by charging by means of the coronadischarge and, when exposed to light, the charge in the exposed area disappears) is formed on a support by incorporating a photoconductive substance into a silicone rubber layer in an amount not in excess of 6 times the weight of the silicone rubber (the photoconductive substance should not show itself on the surface of the photosensitive layer since this reduces the inkrepellent property; it should not be deeper than 4 ,u. in the silcone layer from the surface, because a large distance from the surface lowers the photoconductivity), there can be formed a printing plate having good electrophotographic properties, improved toner fixing capability and sufficient inkrepellancy property by a mono-bath coating. The thickness of the layer in this embodiment is 1 10 t, prferably 3 7 u. The ratio of photoconductive substance/- silicone gum is 6/1 1/3, preferably 4/1 1/2. The photoconductive substance used in the system is preferably zinc oxide or cadmium sulfide, most preferably zinc oxide. This embodiment can involve a very simple onelayer form (see FIGs. 2(a) and.2(b)).

3. When a photosensitive layer composed ofa photoconductive substance is formed on the support, and the silicone rubber layer mentioned in (2) above is then formed on top of the photosensitive layer, there can be formed a printing plate which has especially superior printing resistance. In embodiment (3) the first layer is itself film-forming, e.g., polyvinylcarbazole. The thickness of the first layer is l 5 [.L, preferably 2 4 u. The thickness of the second layer, which is as in embodiment (2), in this embodiment is preferably 0.5 5 11., most preferably 1 2 ,u thick.

4. When a photosensitive (electrophotographically chargeable, etc.) layer consisting of a mixture of an inorganic photoconductive substance such as ZnO and an insulating binder in a ratio of 220:1 (weight/- weight) is formed on the support and on top of the photosensitive layer there is coated a layer of a mixture of photoconductive substance and a one-can silicone rubber of the deoximization or dealcoholization type which is curable at room temperature as in embodiment (2) in a ratio of 6-0.00l:1, there can be formed a printing plate having good electrophotographic plate making capability and ink-repellancy and also having good operability and stability, especially in view of the method of production. The ratio of zinc oxide to insulating binder is preferably 8/1 (by weight) and the film thickness is 1 10 ,u, preferably 2 5 ,u, in the first layer, on which the composition of embodiment (2) is coated in a thickness of, l 5 ;1., preferably 2 4 [.L.

Preferred insulating binders include styrene, phenol resins, epoxy resins, modified alkyd resins (modified by styrene), etc.

The term electrophotographical plate-making property or capability denotes an overall property of the printing plate, whereby the charged plate has good electrical potential decay characteristics upon exposure, the developing toner does not adhere much to the portion having reduced electric potential, and the toner is well fixed to the printing plate by heating or by a chemical means.

The term ink repelling property or capability denotes the property of the printing plate whereby the silicone rubber surface on the plate does not accept ink even in the absence of depening water. Since the ink repelling property is reduced with increasing amounts of the photoconductive substance in the silicone rubber, but the electrophotographic properties are improved, these two properties should be balanced by controlling the amount of the photoconductive substance.

5. The resulting printing plate master prepared by the above method is uniformly charged in a dark place, exposed, developed and fixed to electrophotographically prepare a planographic printing plate (in the strict sense of the word, the printing plate is not a true planar plate, as the toneradhered portion (image area) is convex; however, generally speaking, this also comes within the category of planographic printing plates). Using this planographic printing plate, offset printing or direct printing can be carried out only by inking without the supply of dampening water.

6. It has been found that when a master whose photosensitive layer consists of a kneaded mixture of zinc oxide, preferably in thread-like form, and silicone rubber is used, and after electrophotographic plate making, is treated with an acid, the zinc oxide of the toner-free portion (i.e., the non-image area) is dissolved up to a depth of about 2 p. to leave the silicone rubber at this portion. Consequently, this results in an improvement of the ink repelling property.

The acids used in the acid treatment include both organic acids such as acetic, formic acid and propionic acid, etc., and inorganic acids such as hydrochloric and sulfuric acid. Best results are obtained when the concentration of acid is 50 100% by weight, preferably 80%, of the treating solution using a treatment temperature of from room temperature to 80C, preferably to 50C, for 10 seconds, preferably to 30 seconds.

The structure of the master plate, the method for its production, the method for plate making from the master plate, and the method for printing in accordance with this invention will be further described by reference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 are each sketches showing an example of the plate-making master of this invention;

FIG. 5 shows one example of the printing plate made in accordance with the method of this invention; and

FIG. 6 is a sketch of a printing plate prepared similarly to that shown in FIG. 5, in which the non-image area has been treated with an acid.

DETAILED DESCRIPTION OF THE INVENTION In those embodiments where an inorganic powder such as zinc oxide (photoconductive substance) is dispersed in a binder, the ratio of binder to photoconductive substance is important. Too low an amount of photoconductive substance diminshes the conductivity and too great an amount thereof provides no adhesion to a supporter, though excellent conductivity is provided. For this reason, in several embodiments the ratio of photoconductive substance to binder is 20/1 1/3, preferably 8/1 l/l.

Photoconductive, as is known in the art, defines the following state: a coated photoconductive substance is subjected to corona-discharge, then imagewise exposed so that the exposed area is discharged with remaining charge in the unexposed area. The resulting latent image has a toner applied thereto which is fixed by heating.

Referring to FIG. 1, a layer 2 of a photoconductive substance is formed on a support 1 such as paper, a synthetic resin film or an aluminum plate by any customary method.

This photoconductive layer can be formed from a dispersion of finely divided particles of an inorganic or organic photoconductive substance in an insulating binder, preferably of a particle size of 0.05 2 1.4., most preferably 0.l to 0.5 u, or may consist only ofa photoconductive polymer, e.g., poly-N-vinylcarbazole. A sili cone rubber layer is coated thereon in a thickness of less than M, i.e., 0.5 to 10 microns, preferably 2 to 5 microns. This plate is characterized in that the thickness of the silicone rubber layer can be increased as compared with dry plates, and this contributes to the prevention of scumming due to scratches. Preferably, the silicone rubber is a one-package silicone rubber curable at room temperature, which is diluted with an inert solvent to give a 5 10 wt solution of the silicone rubber, e.g., in nephtha or n-heptane, and then cured by heating,.e.g., at 150 180C for 1 2 minutes, preferably at 180C for 1 minute. In order to improve the adhesion between the layer 2 and the layer 3, it is best to interpose a thin coating of a silicone primer between these layers, for example as thin as an unimolecular film; probably 80 100 A, will suffice in most cases.

Preferred supports in the present invention include synthetic resin films such as polyethylene terephthalate, polycarbonate, cellulose triacetate, etc., Papers such as polyvinyl chloride-coated paper, polyethylenelaminated paper, aluminum foil-laminated paper, etc., with polyethylene terphthalate being most preferred.

In the example shown in FIG. 2(a), a silicone rubber layer 4 including a photoconductive substance 2 is formed on a support 1 similar to that exemplified above. The photoconductive substance and the silicone rubber are mixed in a ratio of 6-0.00lzl, preferably 4-0.5:l. The photoconductive substance is uniformly dispersed in the silicone rubber, but should not be exposed to the surface thereof.

In the example shown in FIG. 2(b), the photoconductive substance is sparsely distributed in the silicone rubber layer 4 on the surface side 4(a) but densely on the side 4(b) toward the support 1. The gradient is not very important so long as there is some gradient. For example, if the viscosity of a mixture of zinc oxide and a heptane solution of a one-package silicone rubber curable at room temperature is properly controlled, and the mixture is coated on the support followed by standing, the zinc oxide, which has a high specific gravity, precipitates in the coated film and congregates at the side of the support as opposed to the surface side. The thickness of the coating in FIGS. 2(a) and 2(1)) may vary. However, since the silicone rubber is not extremely great in mechanical strength, too great a thickness affects the printing resistance of the printing plate and the thickness is preferably 1 10 a, most preferably 2 5 u.

FIG. 3 relates to a self-film-forming organic photoconductive substance such as polyvinyl carbazole. In FIG. 3, a photoconductive substance layer -2 similar to that in FIG. 1 is formed on a support 1. A layer 5 consisting of a mixture of a photoconductive substance and a silicone rubber in a ratio of 6-0.00l:1, preferably 1/3:l is coated thereon (see FI'GS. 2(a) and 2(b), which illustrate this type of layer). The thickness of the layer is not more than 20 microns, best not more than about 10 microns. If the thickness is too large, the electrophotographic properties of the printing plate master are deteriorated.

FIG. 4 teaches a more detailed embodiment of a pro cess as shown in FIG. 2(b). In FIG. 4, a photosensitive layer 6 consisting of a mixture of an inorganic photoconductive substance such as zinc oxide and an insulating binder in a ratio of 2-20:1 is formed on a support 1. On top of the photosensitive layer 2, a layer 7 of a mixture of a photoconductive substance and silicone rubber in a ratio of 6-0001 1 is coated thereby to form a master plate. The thickness of the first or upper layer is preferably l-l0 [.L, most preferably 2 5 p. and the thickness of the second or under layer is preferably 1 5 t, most preferably 2 5 ,u..

The master plates shown in FIGS. 3 and 4 comprise a support, a photosensitive layer thereon which has good electrophotographic characteristics, and an uppermost layer of silicone rubber which has good electrophotographic properties and good ink repelling properties. These plates exhibit good overall electrophotographic properties and ink repelling properties.

The master plates shown in FIGS. 2, 3 and 4 in which a photoconductive substance is incorporated in the silicone rubber layer lend themselves to easier heat-fixing after electrophotographical toner development than that shown in FIG. 1 which includes a pure silicone rubber layer. The reason for this is not known.

The principle of plate making and printing is shown in FIG. 5. The master, including a silicone rubber layer 10, which can be as shown in any of FIGS. 1 to 4, is electrophotographically charged, exposed, developed with a toner, and fixed in accordance with a conventional procedure. The toner adheres firmly even to the silicone rubber layer to form a stable toner image. The portion 30 on the plate which corresponds to an image area 30 of an original 20 has fixed thereto the toner to conceal the silicone rubber surface, while the toner does not adhere to the portion 40 on the plate which corresponds to a non-image area 40' of the original 2 but the silicone rubber surface is revealed thereby to form a printing plate. The ink adheres well to the toner portion, but does not adhere at all to the silicone rubber portion. Since the difference in ink adhering power between these two portions is sufficiently large, the resultant printing plate set on ordinary offset printing presses can give good quality impressions free from scumming or smearing. There is no need to supply dampening water during printing. Furthermore, when this plate is inked using a roll and direct printing on paper is carried out, no scumming or smearing is observed.

FIG. 6 shows a printing plate which has been obtained by electrophotographically developing a plate comprising layer 32 of a photoconductive substance such as zinc oxide and a silicone rubber and a support 1, and then subjecting it to a chemical treatment. After electrophotographic charging, exposure, toner development and heat fixation, the plate is treated with an aqueous solution of an organic or inorganic acid such as a carboxylic acid, e.g., acetic acid or citric acid or hydrochloric acid or sulfuric acid, the toner-adhering portion 30 (corresponding to the image area of the original) does not undergo any change, but the tonerfree portion 40 is affected by the acid and the zinc oxide is dissolved and removed from the silicone rubber layer in area 41 to provide a nearly pure silicone rubber layer. This portion corresponds to the nonimage area of the original, and by the acid treatment, its ink repelling property can be improved. The photoconductor such as zinc oxide in the silicone gum layer is preferably dissolved out from the surface up to l 1.5 n'deep.

The acid is selected considering the photoconductive substance disposed, for example, for zinc oxide, an aqueous O 80 wt solution of acetic acid was used at 50C for 30 seconds.

While zinc oxide (ZnO) has been described above as the photoconductive substance, the invention is not limited thereto, but includes other inorganic substances such as S, Se, CdS, CdSSe, ZnS Ar-Se alloys, Pbl and organic substances such as azoles, anthracenes, triphenylamine or polynuclear aromatic vinyl polymers, e.g., anthraquinone. If desired, the photoconductive substance can contain a sensitizer. All sensitizing dyes as are generally used in the electrophotographic arts can be used, e.g., Fluorescine, Rose Bengal, Eosine, Rhodamine B, Brilliant Green, Thioflavine, Acridine Orange, etc. These are especially effective in combination with ZnO.

ZnO is one of the most useful photoconductive substances with respect to economy, operability, safety and stability. Polyvinyl carbazole, for example, can be used without a binder.

All photoconductive substances which are used in electrophotography, can, in general, be used in this invention. These substances are dispersed in the form of particles or as a monomolecular dispersion in an insulating binder or materials such as polyvinyl carbazole can be applied on a conductive layer by coating without a binder. The size of photoconductive substance dispersed in the form of particle is usually about 0.05 2n, preferably 0.1 0.5a.

The silicone rubber has the property of cross-linking or polymerizing after coating. Two-package silicone rubbers can be used, but one-package silicone rubbers curable at room temperature are more easily used. Curable one-package silicone rubbers of the deoximization or dealcoholization type are especially useful with respect to their comparativility with the photoconductive substance (i.e., dispersibility) and stability. The silicone rubber may contain fillers such as silica. The fillers used are principally SiO (colloidal silica), and/or a pigment (e.g., phthalocyanine) which are generally dispersed in an amount of 2 3% in the silicone rubber. It is convenient to use the silicone rubber in the form of a solution in an inert solvent such as n-hexane, heptane or naphtha. While the silicone rubber can be in the form of a paste without solvent, a solution is better bel Si-O I and a terminal group of the formula:

(R'O) 1 O (AcO) i O r N o)si o or the like,

wherein n is an integer from 2 to about 20,000, R may be the same or different and represents a monovalent alkyl or aryl or cyanoaryl group, and the major part of R is in general methyl, while 2 3% of all Rs can be vinyl, phenyl, halogenated vinyl or halogenated phenyl.

This rubber is called a silicone rubber. The terminal groups can be split off to yield a silicone elastomer having a higher molecular weight. In this case, it is called a deacetic-acid-, dealcoholor deoxime-type, depending on the kind ofgroup split off. ln general, the molecular weight of the silicone rubber is less than l00,000 and the silicone elastomer is an organopolysiloxane having a mean molecular weight of about 400,000 800,000.

These are the types of silicone rubbers used in the Examples, where the terminal group is identified as to the type of group split off during hardening.

The silicone rubber to be used in this invention is most preferably of the dealcoholor deoxime-type.

The insulating binder is preferably selected from natural or synthetic resins, for example, vinyl resins, silicone resins (silicone varnishes), phenol resins, cellu lose derivatives, with nitro cellulose being preferred, styrene rubber or epoxy resins. Of these, vinyl copolymers of the acrylate ester type or modified alkyd resins are useful with respect to solvating power, coatability, stability, and electrical characteristics, with the ethyl ester of polyacrylic acid being preferred. Copolymers of vinyl chloride and vinyl acetate; alkyd, epoxy resins and urethane resins, which are cured with isocyanates,

are also preferred. The binder can be made into a solution and the photoconductive substance dispersed therein by means of a homomixer or ball mill. All insulating binders, which are in general used in the electrophotographic art can be used in the present invention. The binder should have a high insulating property, provide a stable dispersion of the photoconductive substance and be coatable on the support with good adhesion.

The developer is in the form of resin particles containing the particles of a resin and a pigment, and is available commercially from the Xerox Company, Ricoh Company, lwasaki Tsushinki Kabushiki Kaisha, as, for example, Xerox 914 toner, lwasaki Tsushin ELEFAX toner, etc. Preferred of such materials are those exemplified in US. Pat. Nos. 2,788,288 and 3,079,342.

When a primer is used it preferably mainly comprises a carbon-functional silane compound as a 1 50 wt solution in n-heptane, naphtha, isopropanol, etc. The structure of the carbon-functional silanes is as follows:

$011 R $1 OCH OCH where R is :H NCH CH NHCH CH CH Since the plate-making master of this invention has electrophotographic properties, it has high light sensitivity and needs only about one-tenth of the amount of exposure as a conventional presensitized plate (dry plate) which does not require dampening water. Furthermore, since it can be rendered photosensitive by charging in the dark just prior to use, it is not necessary to store it in a light-shielded place, and its shelf life is almost infinite. The use of an intermediate negative or positive is not necessary using the plate of the present invention, i.e., plate making is possible directly from an original. In addition, the plate making procedure is very simple, and the entire plate making process can be effected under dry conditions. The plate making can be easily rendered machine-operable, and no chemicals I which cause environmental pollution need be used.

When the plate-making master of this invention is compared with conventional masters for electrostatic platemaking, there is no difference in high sensitivity, stability and simplicity of the plate-making process, but because dampening water is not required during printing, the master of this invention is far superior to conventional masters with respect to ease of printing and the ease of control of the printing press. The conditions of exposure, etc., in the present invention are not overly critical. Usually a negative charge of 600 800 V, preferably 700 V, is given. Exposure is commonly at 5,000 lux for 2 5 seconds, preferably about 3 seconds. Fixing is generally at 150 180C for 1 2 minutes. These values can vary greatly, depending upon the exact system.

The following examples illustrate the present invention in greater detail. In the examples all parts and percentages are by weight, unless otherwise specified.

EXAMPLE l One part of styrene-modified alkyd resin (Styresol, product ofJapan Reichhold Co., Ltd.) was dissolved in a mixture of 1 part of xylene and 8 parts of toluene. in the resulting solution was dispersed 8 parts of zinc oxide (0.1 0.5 [1. particle size) using a ball mill. The dispersion was coated in a thickness of 10 microns on art paper which had been rendered electrically conductive. A 6% n-heptane solution of Toray Silicone SH 78/RTV (this is a silicone rubber where acetic acid is eliminated upon hardening) was coated on top of the above coating in a thickness of 2 to 4 microns after drying. The solvent was evaporated off at room temperature, and the silicone rubber layer was heated and cured for 10 minutes.

The resulting master plate was exposed electrophotographically in a customary manner (300 800 Volt negative charge; 5,600 lux 2 3 seconds) through an original, developed, and then heat fixed (at 180C for 1 minute). lwasaki Tsushin ELEFAX toner was used in this Example for the development. The resulting printing plate was mounted on an offset printing press from which the dampening water device had been removed, and 1,000 impressions were produced using semi-solid ink (Speedking Ace 90, black, product of Toyo lnk Kabushiki Kaisha).

Unless otherwise indicated in all following Examples exposure, etc., were as defined above.

EXAMPLE 2 In order to increase the adhesion between the zinc oxide layer and the silicone rubber layer in Example 1, a thin layer (50 80 A) of Toray Silicone Primer PRX 304 or styrene-modified alkyd resin was formed between these two layers.

EXAMPLE 3 In Example 1, Toshiba TSE-370 RTV (silicone rubber where acetic acid is eliminated from the end portions to give a silcone elastomer) was used as the silicone rubber, otherwise, the procedure of Example 1 was repeated. Equivalent results were obtained.

EXAMPLE 4 F our parts of zinc oxide (0.1-0.5a particle size) was added to a solution of 1 part of a one-package silicone rubber curable at room temperature (Toray Silicone Company, Toray Silicone SH 780 RTV; silicone rubber where oxime is eliminated from the end portion during hardening) in 4 parts of n-hexane, and dispersed therein by a homogenizer. The resulting dispersion was coated on an aluminum plate using a No. 18 coating rod, followed by curing at C for 10 minutes. The thickness of the coating after drying was about 10 microns. The aluminum plate had been grained and treated with silicate, and coated with a primer by applying a 10% toluene solution of styrene-modified alkyd resin thereto.

The resulting master was negatively charged by corona discharge in the dark using an e1ectrophotographic device in a customary manner, and exposed through an original using an optical system. A charged pattern corresponding to the image of the original was formed on the plate. The plate was then developed with a positive toner (lwasaki Tsushin EKEFAX toner toner; carbon black coated with polystyrene) and then fixed by heating at 180C for one minute. When the plate was placed on a flat stand and inked, the ink adhered well to the portion to which toner was adhered (the portion corresponding to the image area of the original), while the toner-free portion (the portion corresponding to the non-image area of the original) completely repelled the ink since the silicone rubber was exposed. The inked pattern was transferred to white paper. By direct printing, more than 200 impressions could be produced.

EXAMPLE Six parts of styrene-modified alkyd resin as a binder, 50 parts of toluene as a solvent therefor, and 40 parts of zinc oxide (Sasex 2000, Sakai Chemical Co., Ltd.; 0.1 0.5 1. particle size) as an inorganic photoconductive substance were mixed by a homogenizer for 20 minutes to form a dispersion. The resulting dispersion was coated on the aluminum surface of a polyester film (Metalmi, product of Toray Industries, lnc., polyester on which aluminum had been deposited) in an amount of 20 g/m 4.5 parts of a one-package silicone rubber curable at room temperature (Toray Silicone SH 780 RTV, product of Toray Silicone Company), 3 parts of zinc oxide as above and 20 parts of n-heptane were mixed and dispersed by a homogenizer. The resulting dispersion was coated on top of the above coating in an amount of 8-12 g/m and cured at 120C for minutes to form a plate-making master.

The master was subjected to dark adaptation and the photosensitive layer thereof uniformly charged to 300 volts by negative corona discharge. The plate was then exposed for 2 seconds in a darkroom by bringing a transparent positive line figure into intimate contact with it using a printer (for quick copies, product of Fuji Photo Film Co., Ltd.) with a luminosity of 5,600 lux. The plate was then developed with a styrene toner available from Xerox Company (Xerox 914 toner) by a cascade development, and the heated at 180C for 1 minute to fix the toner and thereby form a printing plate.

This printing plate was mounted on an offset printing press from which the dampening water supply device had been removed and printing was carried out using ink for dryography (Sun Chemical). More than 1,000 impressions of good quality could be produced. When an offset roller was also removed from the printing press and the printing plate was inked, there could be obtained impressions by direct transfer ofthe ink to paper.

EXAMPLE 6 Example 4 was repeated except that a grained aluminum plate for use in general presensitized plates, or art paper which had been rendered electrically conductive, was used. Equivalent results were obtained.

EXAMPLE 7 Example 4 was repeated except that the silicone rubber layer was produced as follows: 2 parts of polyvinyl anthracene (a photoconductive substance disclosed in Japanese Pat. Publication No. 27588/68) was dispersed in a solution of 10 parts of silicone rubber (KB 44 or 45, of Shinetsu Chemical Co., Ltd.; silicone rubbers where oxime is eliminated from the tip portion during hardening) in 40 parts of'n-heptane. The resulting dispersion was coated on the support at a rate of 8 g/m Equivalent results were obtained.

EXAMPLE- 8 The printing plate made in Example 3 was immersed in a 30% aqueous solution of acetic acid at room temperature for 30 seconds. Zinc oxide present near the surface of the non-image area was dissolved. After washing with water, the plate was immersed for 10 seconds in n-heptane, and dried. The ink repelling property of the non-image area was especially improved.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What we claim is:

l. A method for producing a printing plate that does not require dampening water during printing, which comprises electrostatically charging a plate-making master, said master comprising a support and a photosensitive layer formed thereon consisting essentially of a mixture of a photoconductive substance and a silicone rubber in a ratio of 6-0.1:1, uniformly in a dark place, exposing it through an original, developing it with a toner, fixing the toner by heating thereby to form on said master an ink receptive portion having the toner adhered thereto and an ink repelling portion free from the toner, and then treating the resulting plate with an acid to thereby dissolve the photoconductive substance at the portion free from the toner.

2. The process of claim 1 wherein zinc oxide is used as the photoconductive substance.

3. The process of claim 1 wherein a one-package silicone rubber curable at room temperature is used as the silicone rubber.

4. The process of claim 1 wherein a two-package silicone rubber is used as the silicone rubber.

5. A method for producing a printing plate that does not require dampening water during printing, which comprises electrostatically charging a plate-making master, said master comprising a support, a photosensitive layer formed thereon and having photoconductivity, and a layer, formed on said photosensitive layer, consisting essentially of a photoconductive substance and a silicone rubber in a ratio of 6-0.1:1, uniformly in a dark place, exposing it through an original, developing it with a toner, fixing the toner by heating thereby to form on said master an ink receptive portion having the toner adhered thereto and an ink repelling portion free from the toner, and then treating the resulting plate with an acid to thereby dissolve the photoconductive substance at the portion free from the toner.

6. The process of claim 5 wherein zinc oxide is used as the photoconductive substance.

7. The process of claim 5 wherein a one-package silicone rubber curable at room temperature is used as the silicone rubber.

8. The process of claim 5 wherein a two-package silicone rubber is used as the silicone rubber.

9. A method for producing a printing plate that does not require dampening water during printing, which comprises electrostatically charging a plate-making master, said master comprising a support, a photosensitive layer formed thereon consisting essentially of a mixture of an inorganic photoconductive substance and an insulating binder in a ratio of 2-20: I and a layer formed thereon consisting of a photoconductive substance and a silcone rubber in a ratio of 6-0.01:1, uniformly in a dark place, exposing it through an original, developing it with a toner, fixing the toner by heating thereby to form on said master an ink receptive portion having the toner adhered thereto and an ink repelling portion free from the toner, and then treating the resulting plate with an acid to thereby dissolve the photoconductive substance at the portion free from the toner.

10. The process of claim 9 wherein zinc oxide is used as the photoconductive substance.

11. The process of claim 9 wherein a member seicone rubber is used as the silicone rubber. 

1. A METHOD FOR PRODUCING A PRINTING THAT DOES NOT REQUIRE DAMPENING WATER DURING PRINTING, WHICH COMPRISES ELECTROSTATICALLY CHARGING A PLATE-MAKING MASTER, SAID MASTER COMPRISING A SUPPORT AND A PHOTOSENSITIVE LAYER FORMED THEREON CONSISTING ESSENTIALLY OF A MIXTURE OF A PHOTOCONDUCTIVE SUBSTANCE AND A SILICONE RUBBER IN A RATIO OF 6-0.1:1, UNIFORMLY IN A DARK PLACE, EXPOSING IT THROUGH AN ORIGINAL DEVELOPING IT WITH A TONER, FIXING THE TONER BY HEATING THEREBY TO FORM ON SAID MASTER AN INK RECEPTIVE PORTION HAVING THE TONER ADHERE THERETO AND AN INK REPELLING PORTION FREE FROM THE TONER, AND THEN TREATING THE RESULTING PLATE WITH AN ACID TO THEREBY DISSOLVE THE PHOTOCONDUCTIVE SUBSTANCE AT THE PORTION FREE FROM THE TONER.
 2. The process of claim 1 wherein zinc oxide is used as the photoconductive substance.
 3. The process of claim 1 wherein a one-package silicone rubber curable at room temperature is used as the silicone rubber.
 4. The process of claim 1 wherein a two-package silicone rubber is used as the silicone rubber.
 5. A method for producing a printing plate that does not require dampening water during printing, which comprises electrostatically charging a plate-making master, said master comprising a support, a photosensitive layer formed thereon and having photoconductivity, and a layer, formed on said photosensitive layer, consisting essentially of a photoconductive substance and a silicone rubber in a ratio of 6-0.1:1, uniformly in a dArk place, exposing it through an original, developing it with a toner, fixing the toner by heating thereby to form on said master an ink receptive portion having the toner adhered thereto and an ink repelling portion free from the toner, and then treating the resulting plate with an acid to thereby dissolve the photoconductive substance at the portion free from the toner.
 6. The process of claim 5 wherein zinc oxide is used as the photoconductive substance.
 7. The process of claim 5 wherein a one-package silicone rubber curable at room temperature is used as the silicone rubber.
 8. The process of claim 5 wherein a two-package silicone rubber is used as the silicone rubber.
 9. A method for producing a printing plate that does not require dampening water during printing, which comprises electrostatically charging a plate-making master, said master comprising a support, a photosensitive layer formed thereon consisting essentially of a mixture of an inorganic photoconductive substance and an insulating binder in a ratio of 2-20:1, and a layer formed thereon consisting of a photoconductive substance and a silcone rubber in a ratio of 6-0.01:1, uniformly in a dark place, exposing it through an original, developing it with a toner, fixing the toner by heating thereby to form on said master an ink receptive portion having the toner adhered thereto and an ink repelling portion free from the toner, and then treating the resulting plate with an acid to thereby dissolve the photoconductive substance at the portion free from the toner.
 10. The process of claim 9 wherein zinc oxide is used as the photoconductive substance.
 11. The process of claim 9 wherein a member selected from the group consisting of vinyl resins, silicone resins, phenol resins, cellulose derivatives, styrene rubbers and epoxy resins is used as the binder.
 12. The process of claim 11 wherein a vinyl copolymer containing acrylic ester units or a modified alkyd resin is used as the binder.
 13. The process of claim 9 wherein a one-package silicone rubber curable at room temperature is used as the silicone rubber.
 14. The process of claim 9 wherein a two-package silicone rubber is used as the silicone rubber. 